Photoelectric relay



57 RUBEN jam, 1 I1, 1938 PH-QTOELECTRIC RELAY Filed Feb. '7, 1956 INVENTOR mi MUfL RUBEN I BY GHQ,

' ATTORNEY Patented Jan. 11, 1938 UNlTED STA'EEEi PATENT OFFIE 2 Claims.

This inventionv relates to a photoelectric relay, and more particularly it relates to a photo-sensitive relay device having a photoelectron emission cathode and an anode which is thermomechanically sensitive to electron bombardment. Broadly, the device of this invention is of the type described in my United States Letters Patent 1,847,669, in which is described a thermostatic element which is used to control a local circuit by 7 means of its electron bombardment from a thermionic cathode.

An. object of this invention is the provision of a device for controlling a relatively large current in a local circuit by means of the illumination of the cathode element.

Other objects will be manifest from reading the specification.

In the present invention photo-electron emission is employed in place of the thermionic emission for actuating a thermc-sensitive anode which controls a local circuit.

The cathode is a plate, preferably tungsten, coated with caesium metal derived from the salt, and a reducing agent, such as caesium, nitrate and magnesium powder. For greater access of light to the caesium-coated cathode surface and to reduce its mass the anode, consisting of a thermostatic material, is perforated; it has mounted thereon a movable contact. The combination preferred for the anode material is invar and steel.

The preferred method of coating the cathode is, after the tube elements have been completely de-gassed by inductive heating under a. high vacuum, to reduce within the envelope a caesium salt in combination with a reducing agent, such as caesium nitrate and magnesium powder. This mixture is vacuum sealed in a glass tube which, in turn, is within a thin walled nickel cylinder. In the preparation of the device, at the proper time, the nickel cylinder is inductively heated to a temperature sufiiciently high to cause a re-action between the caesium salt and the magnesium, on the occurrence of which the high vapor pres sure of the caesium bursts the glass tube, the caesium escaping through openings in the nickel tube and condensing on the cathode and other surfaces. The coating is removed from the other elements by heating them to a proper temperature to re-condense the caesium upon the cathode suriace. While caesium is preferred as the coating material for the cathode, other photoelectron emission alkaline materials, such as rubidium, sodium and potassium can be used, all of which I have employed experimentally.

For a better understanding of the invention reference is made to the accompanying drawing in which E is the plate cathode coated with an electron emission deposit of caesium, 2 a perforated thermostatic anode carrying a movable contact 3, the stationary contact 4 being mounted on conductive support 4a, all contained within glass tube 5. At '5 and t are the terminals of the local circuit to be controlled and at 9 is a source of potential for accelerating the electron discharge to the anode. At id and H are leads to the cathode and anode respectively, l2 indicating the capsule containing the caesium salt.

In the operation of this device, under the infiuence of illumination of the cathode which is maintained at a negative potential of preferably 400 volts in respect to the thermostatic anode, there is an electron. emission from its surface, the electron bombardment against the anode causing that element to become heated and to thermostatically move the contact mounted upon it toward the stationary contact and to thereby close the local circuit. A grid (not shown) may be interposed between the cathode and anode to vary the electric field between. those elements, if so desired. And other thermosensitive movements of the anode element may be used, such as its direct thermal expansion under the influence of the electron bombardment, or the local circuit may be controlled by a critical or snap movement of the thermostatic anode induced by the electron bombardment.

What I claim is:

l. A relay having in an envelope a cathode having a photo-electron emission surface, a thermostatic anode plate having apertures therein and mounting a contact for an external electric circuit separated by a gap from another contact mounted in a fixed position in the envelope, the first mentioned contact being movable to open and close the gap in response to variations in the electron bombardment of the anode under the infiuence of changes in light impressed upon said photo-electron emission cathode surface.

2. A relay comprising essentially a two-element device housed in a closed envelope, one element being a cathode having an electron emitting surface coated with a photo-sensitive substance and the other element being an anode thermally responsive to electron bombardment, said anode having a movable contact, and a fixed contact spaced adjacent said movable contact.

SAMUEL RUBEN. 

